So every time you open a door or a window in your home "the indoor air quality immediately mimics the outdoor air quality" - simply put, if the pollution levels outdoors are high, they'll instantly become high indoors too.

And the question then is: can you sit pretty much all the time in a room that's completely shut off?

"It's not really practical," says Dr Madan.

Face masks

Online retailers in India have thousands of options for masks. You can also buy them at your neighbourhood chemists.

Some are simple cloth masks while others come with high-grade filters to keep toxins out. They're available in black or can be multi-coloured.

And thousands of people in the capital, which is among the worst affected by pollution, are wearing them.

But can a face mask protect you from the deadly tiny particulate matter that enter deep into the lungs and play havoc with your health?

A mask with a capacity to filter out these tiny microns can help but, Dr Madan says, they will have to be worn all the time and be completely sealed around the nose and the mouth.

"But these high filtration capacity masks can make breathing difficult, especially during exercise. And how are you going to make children wear it when they go out to play?

"These are solutions that are very difficult to use," he adds.

Gooseberries and turmeric

Last week, as Delhi's air quality began worsening, schools in Delhi started taking precautionary measures - morning assemblies were suspended, outdoor games were restricted, and one school began distributing gooseberries to students.

That's because traditional Indian wisdom says the sour green fruits are loaded with anti-oxidants and can help boost immunity and reduce the impact of pollution.

Nutritionists have also suggested drinking a concoction made with turmeric, ginger and Indian basil, or eating jaggery or clarified butter.

Image copyrightAFPImage caption
Doctors say the number of patients with respiratory problems has risen in the past week

Dr Madan says he's not sure to what extent these claims are backed by scientific data and that there is no evidence to suggest they work.

He says any food that contains vitamins and anti-oxidants is good for overall health, but it doesn't prevent exposure to pollution.

In the past week, Dr Madan says, the number of patients he's seen with "asthma-like symptoms" has risen, with many complaining about a "burning-itching sensation in the nose and throat".

Describing it as a "serious health emergency", he says children, the elderly and the asthmatic are more vulnerable to bad air and he's advising them to "avoid outdoor activities and heavy exertion".